1. Field of Commercial Utilization
This invention relates to an emulsion ink for stencil printing. More particularly, it relates to an emulsion ink for stencil printing, which affords a printed image having a high density and a constant quality, without being influenced by the kinds of printing paper and the presence or absence of projections and depressions on the surface of printing paper, and has a superior ink-drying property and no exudation, seeping-through and offsetting of ink.
2. Description of the Related Art
Stencil printing is conducted by using stencil sheet, feeding an ink through the perforated parts formed on the sheet, to carry out printing on the body to be printed, such as paper; hence the stencil printing has been utilized in broad fields due to the easy stencil-making.
As the ink used for stencil printing, water-in-oil(W/O) type emulsion ink has been generally used. The drying of this emulsion ink is carried out by impregnating the ink component into the inside of the printing paper as the body to be printed and at the same time, scattering water component into the air (see Japanese patent application laid-open Nos. Sho 61-255967, Sho 64-14284, Hei 4-132777, Hei 5-117565, etc.).
However, in the case of conventional W/O type emulsion ink which contains a coloring agent, the ink component is impregnated into the inside of the printing paper at the time of ink drying, and at the same time, the coloring agent, too, is impregnated into the inside of the printing paper; hence there have been raised problems that the quantity of the coloring agent remaining on the surface of the paper is reduced and the printing density is reduced. Further, since the coloring agent in the ink is impregnated into the inside of the printing paper, a phenomenon is liable to occur that a printing image as a counter image is seen from the back surface of the printing paper, that is, the so-called ink seeping-through phenomenon.
Further, the impregnation speed of the ink component into the inside of the paper varies depending upon the kinds of the paper used; hence there occurs a drawback that the density of printed image, and the exudation of ink, seeping-through and offsetting of ink resulting from the different kinds of used paper vary depending upon the kinds of the paper used. Namely, when a paper to be printed has a rapid impregnation speed of ink, the ink component almost dose not remain on the surface of the paper, but it is impregnated into the inside of the paper; hence the printing density of the printed image lowers and the seeping-through of ink increases, and as the ink component does not remain on the surface of the paper, the offsetting decreases. Whereas, when a paper to be printed has a low impregnation speed, the ink components is liable to remain on the surface of the paper; hence the printing density of the printed image becomes high and the seeping-through is decreased, but the ink component remains in a large quantity on the surface of the paper; hence the offsetting of the ink increases. Accordingly, there has been desired an emulsion for stencil printing that a printing image having a high density is obtained without being influenced by the impregnation speed of the ink into the printing paper used, and at the same time, does not cause any seeping-through and offsetting of the ink.
Further, the drying of the emulsion ink is carried out by impregnating the ink into the inside of the paper, hence if stencil printing is carried out by using a printing paper having projections and depressions on the surface of the paper, it is difficult to obtain a printing image of gloss tone, depending upon the kind of paper. Such a phenomenon is observed even in the cases of high quality paper or intermediate quality paper, and it is notable particularly in the case of low quality paper. Thus, the quality of the resulting printing image varies depending upon the presence or absence of the projections and depressions on the surface of the used paper, and such a phenomenon notably appears when full color printing is carried out.
Further, in the case of stencil printing, since the ink is extruded through the perforated parts of the stencil sheet and fed to the printing paper, a certain extent of viscosity should be imparted to the ink. However, if the viscosity is imparted by containing a high molecular weight compound such as resins, in the oil phase component, the impregnation speed of the ink is lowered and the offsetting is liable to occur.
The present inventions have proposed a W/O type emulsion ink for stencil printing having a extender pigment contained in an aqueous phase, thereby affording a good printed image, without being influenced by the impregnation speed of the ink into the printing paper (see Japanese patent application No. Hei 7-24373). However, the following fact has been found: when the emulsion ink is impregnated into the printing paper used, impregnation of the aqueous phase occurs after impregnation of the oil phase; hence the impregnation speed of the emulsion ink is most influenced by the oil phase component; thus, even if a extender pigment is contained in the aqueous phase, the impregnation speed of the ink and the drying property of the ink cannot be improved. As a result, the effect for preventing the offsetting of the ink is limited.